In the early 1980s, managers at the National Aeronautics and Space Administration (NASA) estimated that the flights would be 99.999 percent reliable, which represents a failure rate of only 1 in 100,000. According to the physicist Richard Feynman, who was a member of the commission that investigated the January 1986 Challenger accident, in which the shuttle broke apart shortly into its flight, killing all seven astronauts on board, this “would imply that one could put a Shuttle up each day for 300 years expecting to lose only one.” He wondered, “What is the cause of management’s fantastic faith in the machinery?” Engineers, who were more familiar with the shuttle itself and with machines in general, predicted only a 99 percent success rate, or a failure every 100 launches. A range safety officer, who personally observed test firings during the developmental phase of the rocket motors, expected a failure rate of 1 in 25. The Challenger accident proved that estimate to be the actual failure rate, giving a success rate of 96 percent after exactly 25 launchings.
Past successes may be inspirational and encouraging, but they are not by themselves reliable indicators of or guides to future success. The most efficacious changes in any system are informed not by successes but by failures. The surest way for the designer of any system to achieve success is to recognize and correct the flaws of predecessor systems, whether they be in building codes or in banking policies or in bridges.25 The history of civilization itself has been one of rises and falls, of successes and failures. Some of these have been of empires, dynasties, families; others have been of nations, states, and cities. Common to all of them has been the human element, embodied in the ruler and the ruled alike. Given that the ultimate unit of civilization is the individual, we need look no further than within ourselves to gain insight into the world and its ways, including the failure of its institutions and its systems. And, just as those institutions and systems are made up of individual people and things, so ultimately must we look to ourselves and to how we interact with the world, both given and made, whenever something goes wrong.
In order to understand how engineers endeavor to insure against such structural, mechanical, and systems failures, and thereby also to understand how mistakes can be made and accidents with far-reaching consequences can occur, it is necessary to understand, at least partly, the nature of engineering design. It is the process of design, in which diverse parts of the 'given-world' of the scientist and the 'made-world' of the engineer are reformed and assembled into something the likes of which Nature had not dreamed, that divorces engineering from science and marries it to art. While the practice of engineering may involve as much technical experience as the poet brings to the blank page, the painter to the empty canvas, or the composer to the silent keyboard, the understanding and appreciation of the process and products of engineering are no less accessible than a poem, a painting, or a piece of music. Indeed, just as we all have experienced the rudiments of artistic creativity in the childhood masterpieces our parents were so proud of, so we have all experienced the essence of structual engineering in our learning to balance first our bodies and later our blocks in ever more ambitious positions. We have learned to endure the most boring of cocktail parties without the social accident of either our bodies or our glasses succumbing to the force of gravity, having long ago learned to crawl, sit up, and toddle among our tottering towers of blocks. If we could remember those early efforts of ours to raise ourselves up among the towers of legs of our parents and their friends, then we can begin to appreciate the task and the achievements of engineers, whether they be called builders in Babylon or scientists in Los Alamos. For all of their efforts are to one end: to make something stand that has not stood before, to reassemble Nature into something new, and above all to obviate failure in the effort.